1. Field of the Invention
This invention involves the re-insertion of Video Blanking Interval (VBI) data into a video signal using an On-Screen Display (OSD) processor.
2. Related Art
A single video image as seen on a television screen is called a frame. Thirty (30) frames appear per second. A frame consists of two (2) interlaced vertical fields; an odd field and an even field. The image frame is scanned twice at a 60 Hz rate, once for each field. The lines of the second field are offset to fall between the lines of the first field in a process called interlacing. For a National Television Systems Committee (NTSC) standard frame of 525 lines, each vertical field will have 262.5 lines.
After scanning each field, the electron gun used to illuminate the image inside a television monitor's cathode ray tube (“CRT”) must move back up to the top of the tube to begin the next field. In order to prevent unwanted illumination of the CRT during this vertical retrace, the signal must remain blank until the gun is in position to begin scanning the next field. Accordingly, at the beginning of each vertical field, a period equal to several horizontal lines (40 lines under NTSB standards) is used for a vertical blanking interval, which corresponds to the amount of time it takes the electron gun to return to the top of the screen.
The vertical blanking interval (VBI) portion of the television signal is commonly used to carry information other than video or audio, such as closed-captioned text or stock market data. Such data is called VBI data. It generally originates at an uplink or original video source.
In digital systems, VBI data is transmitted separately from the general video signal, in order to conserve bandwidth. Accordingly, systems have been developed for the reinsertion of the VBI data into the video signal, as that signal is processed. These systems generally require separate, additional components or modules in the receiving hardware.
VBI data is seldom if ever compressed, since it can be more than adequately transmitted in 2 to 48 bytes of data. Frequently VBI data is simply sent with header information in digital broadcasting bitstreams. It generally has packet identifiers that are different than the basic video bitstream. VBI data such as “line 21,” “WINK,” “AMOL,” are sent according to known standards, such as EN 301-775 or ATSCA 53. They are sent with different packet identifiers than media content data. Proprietary standards may also be used.
Because the VBI data is separately transmitted, separate hardware has had to be developed in order to re-insert it into the general video signal at the receiver. The typical approach was to use the video encoder (DENC). This works for analog systems, but not for digital video output streams. Accordingly, other hardware had to be developed such as with Field Programmable Gate Arrays. Later, decompression chips have been developed that had a separate component for generating VBI waveforms for VBI insertion. As a result, expense and complexity for such hardware has increased. There is a need in the industry for more efficient, faster and more economical method and apparatus for the reinsertion of VBI data.
Separately, it is typical for television equipment to display other information on the display screen during the viewing of a program. This information may include text menus, as for programming guides, graphics such as a logo, or local weather announcements. Since this data generally originates locally, from sources other than the original source of the video, separate processing components have been developed for its display. In particular, On-Screen Display, (OSD), is executed by a component usually included on the decompression chips used for decompressing digital video signals such as digital MPEG. OSD processors typically overwrite video in order to display text on the video screen. Typically, a decompression chip prepares bitmap data for the display of a field of video, and then the OSD processor sums in the OSD data to overwrite the video data.
OSD components vary, however they generally provide for the storage or repeated regeneration of the following: a gray scale (or color) palette, dimensions for the size of the OSD text to be displayed and a location for it to be displayed. Typically an OSD controller is combined with an OSD data area in an Application Specific Integrated Chip (ASIC), all of which are usually supplemental to the decompression functions of the same ASIC.